Electricity: motive power systems – Positional servo systems – With particular motor control system responsive to the...
Reexamination Certificate
1999-12-10
2001-04-24
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Positional servo systems
With particular motor control system responsive to the...
Reexamination Certificate
active
06222340
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a control device for a stepping motor, and a driving device for an optical head employing the control device for the stepping motor.
BACKGROUND ART
A stepping motor has characteristics of being small, and having high torque and long life-time. A driving method by an open-loop control utilizing simple controllability of the stepping motor is generally employed therefor. However, in the driving by the open-loop control, there are some problems such as a loss of synchronism wherein a rotation angle of the motor departs from the target, a vibration of the motor, a difficulty in achieving a high-speed rotation, etc. On the other hand, in a driving method by a closed-loop control, an encoder is provided to the stepping motor, and the motor is controlled while detecting the rotation angle of the motor by the encoder, whereby the loss of synchronism and the vibration are suppressed and the high-speed rotation potential improves, though a control system therefor becomes complex.
U.S. Pat. No. 4,963,808 describe a configuration capable of utilizing a two-phase stepping motor in the two types of operation modes while switching the open-loop control with the two-phase stepping motor and the closed-loop control employing the two-phase stepping motor as a DC motor. In addition, also described herein is a technique in which the number of output pulses in one cycle of the encoder for detecting the rotation angle of the stepping motor is set to be a multiple of the number of magnetic poles in the rotor of the stepping motor. The stepping motor is one-phase excited so as to start the rotation of the rotor from the state in which the rotor is at rest in a predetermined position. An exciting current of the stepping motor is switched every time a predetermined number of pulses are output from the encoder in response to this rotation, thereby suppressing a phase difference between the output pulse and the exciting current of the stepping motor to a predetermined error or less without adjustment.
FIG. 7
shows the conventional device for closed-loop controlling the stepping motor.
In
FIG. 7
, a control section
124
drives and controls a stepping motor
125
according to either of a first operation mode and a second operation mode. In the first operation mode, the microstep driving, for controlling the rotation angle of a rotor
129
of the stepping motor
125
by the closed-loop control, in which a current command is output from the control section
124
to a driving section
121
, is conducted at a timing at which the current command is generated by the control section
124
. Furthermore, in the second operation mode, the rotor
129
of the stepping motor
125
is rotated at a high speed by a closed-loop control in which the rotation angle of the rotor
129
is detected by an encoder
128
, the detected rotation angle is provided to the control section
124
, and a current command is output from the control section
124
to the driving section
121
.
The driving section
121
includes an A-phase current driver
122
and a B-phase current driver
123
, which are independent from each other. The A-phase current driver
122
and the B-phase current driver
123
are provided with an A-phase current command and a B-phase current command from the control section
124
through a data selector
137
to form currents of the current commands, respectively, and provide these currents to an A-phase stator
126
and a B-phase stator
127
, thereby driving the stepping motor
125
. Specifically, the A-phase current driver
122
and the Bphase current driver
123
include a D/A converter for converting digital data representing the A-phase current command and the B-phase current command to analog signals, and an amplifier for amplifying and outputting the analog signal.
The stepping motor
125
is of a two-phase PM type, and a stepping angle by the two-phase excitation is 18°. The stepping motor
125
includes a rotor
129
made of a permanent magnet, in which N-poles and S-poles are polarised at every angle of 72° and five poles are polarised for the N-pole and the S-pole in one round, and a two-phase excitation coil including the A-phase stator
126
and the B-phase stator
127
. The A-phase stator
126
and the B-phase stator
127
include yokes in which N-poles and S-poles are polarised at every angle of 72° and five poles are polarised for the N-pole and the S-pole in one round, and these yokes are positioned around the rotor
129
. The magnetic poles of the yoke of the A-phase stator
126
and the magnetic poles of the yoke of the B-phase stator
127
are offset with respect to each other by 18°.
A slit disc
131
, in which slits are formed at every angle of 4.5°, is fixed to a rotor axis
130
. A pitch of an angle of 4.5°, at which each slit of the slit disc
131
is formed, is determined such that it becomes 1/integer of a pitch of an angle of 72° at which each magnetic pole of the rotor
129
is formed (herein, {fraction (1/16)}). Especially, since the number of phases of the stepping motor
125
is two phases, the pitch of the angle of 4.5° at which each slit is formed is determined so as to satisfy a relationship of 1/(a multiple of 2), i.e., {fraction (1/16)}=1 /(2×8).
A photosensor
132
includes an LED of light emission side and a phototransistor of light reception side, and is of a transparent type in which the LED and the phototransistor are placed on both sides of the slit disc
131
. The phototransistor detects the slit of the slit disc
131
by receiving light output from the LED with the phototransistor through the slit of the slit disc
131
. The phototransistor outputs an output signal according to the presence and absence of the slit of the slit disc
131
. The photosensor
132
is contained in the housing
133
with the slit disc
131
, thereby being protected from stain and damage caused by breakage and/or dust.
An output of the photosensor
132
is binarized by a comparator
134
. The comparator
134
not only simply compares the output of the photosensor
132
with a reference value so as to output signals of a high level and of a low level, but also switches the high level and the low level of the output signal only when the output of the photosensor
132
is changed between two reference values, thereby avoiding a malfunction due to chattering.
A pulse signal output from the comparator
134
is input to a control section
124
and a hexadecimal counter
135
.
A counter
135
counts up in the range of an enumerated value 0-15 every time a single pulse signal is input from the comparator
134
; and after the enumerated value reaches 15, the counter
135
initializes the enumerated value to be 0 at a timing of the next count-up, and outputs the enumerated value circulating in the range from 0 to 15 as a binary number of 4 bits. Furthermore, when the clear signal is input from the control section
124
, the counter
135
initializes the enumerated value thereof to be 0.
A 4 input/4 output code converter
136
is provided with an enumerated value of four bits from the counter
135
, converts the enumerated value to a code of four bits, and outputs this code. The relationship between these enumerated values and the code is shown in a code table
81
of FIG.
8
. Herein,
4
bits representing codes output from the code converter
136
are referred to as a P bit, a Q bit, a P inverted bit, and a Q inverted bit. A discrete value input to the code converter
136
is represented not by an actual binary number of 4 bits but by a decimal number.
As seen from the code table
81
, each of bits representing codes output from the code converter
136
is one that is obtained by dividing cycles of a pulse signal output from the comparator
134
so as to be {fraction (1/16)}. Phases of the P bit and the Q bit from the code converter
136
are offset with respect to each other by four cycles of a pulse signal output from the comparator
134
. Likewise, phases of other P invert bit and Q invert bit from the code converter
136
are offset wit
Kawabata Toru
Mushika Yoshihiro
Shioya Masayoshi
Matsushita Electric - Industrial Co., Ltd.
Renner Otto Boisselle & Sklar
Ro Bentsu
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